Almost six years after Lehman Brothers Holdings filed for the largest bankruptcy in history and triggered a global market meltdown, hedge funds are still feeding on its remains. A few firms that waded into the morass following the financial crisis and have spent years analyzing the bankruptcy have made billions of dollars trading in Lehman's debt. And as they collect on claims or sell them, investors are buying ones that come on the market. The value of Lehman debt has risen about 45% since the beginning of 2013, according to a Paulson & Co letter to investors. The $21.4 billion hedge fund firm, which held more than $750 million of the claims at the end of 2013 and at one point was the largest creditor in the bankruptcy, anticipates returns will keep coming.